# Getting started

Use Polyester's tag-value FIX interface for institutional trading connectivity.

FIX Classic provides institutional connectivity for firms that operate established FIX session and tag-value message workflows.

> **Your session package is authoritative**
>
> Use the Polyester dictionary and session profile assigned to your connection. Generic FIX dictionaries do not define the fields, workflows, or limits enabled for your session.

## When to use FIX Classic

Use FIX Classic when your integration requires:

- established FIX session tooling
- operational sequence and recovery workflows
- institutional onboarding and certification
- integration with existing order-management infrastructure

Use [FIX-SBE](https://testnet.polyester.com/docs/developer-docs/fix-sbe/getting-started) when you need FIX session behavior with fixed-layout binary application messages.

## Integration flow

1. Review the session package

   Confirm the assigned FIX versions, dictionary, CompIDs, endpoint, authentication method, enabled business workflows, and operational limits.

2. Implement session behavior

   Implement logon, heartbeat, sequence persistence, resend, reset, logout, and recovery exactly as defined by the session profile.

3. Validate application messages

   Generate or configure message types from the assigned Polyester dictionary. Reject messages that do not match the required fields, enums, and extensions.

4. Complete certification

   Run the conformance and recovery cases for the assigned workflows before connecting the production session.

## Recovery boundaries

## Session recovery

Persist sequence state and follow the assigned resend and reset policy. Session recovery restores FIX protocol sequence.

## Application state

Protocol recovery does not necessarily provide a complete trading snapshot. Reconcile application state through the assigned FIX workflow or Polyester read APIs.

See the [Connectivity matrix](https://testnet.polyester.com/docs/developer-docs/getting-started/connectivity-matrix) to combine FIX with REST, ConnectRPC, or WebSocket realtime.